The use of the kinetic energy in the earth's atmosphere to perform useful work has been practiced for many hundreds of years. This use is carried out by windmills which extract wind power from horizontal air movements along the earth's surface due to atmospheric energy changes.
In the past, windmills have usually extracted power from the wind by propellors in the form of sails, flats, or foils, positioned on rotary mounts in a vertical plane for rotation about a horizontal axis. Such prior art windmills also usually include an appropriate tracking mechanism which acts continually to turn the propellor unit into the wind.
With the development of the airfoil propellor for aircraft, this form of propellor has come into widespread use in windmills for the last 50 years.
Windmills for the generation of electric power have been introduced into commercial use with the advent of the storage battery. The propellors for such windmills are usually mounted directly on the shaft of an electric generator, and the resulting power plant constitutes an inexpensive source of electric power, in which the batteries are charges so long as the wind is blowing to store electricity for use on calm days.
In the operation of a windmill, the rotating vanes intercept a mass of air entering at a given velocity. Adjacent air moves at a constant velocity past the area swept by the vanes, but the intercepted air decellerates in transferring energy to the vanes. This decellerated portion of the air must retain enough velocity to exit from the vanes. This means that the windmill cannot extract all the kinetic energy from the approaching wind. However, downstream from the windmill, the decellerated air mixes turbulently with the adjacent air, and the resulting energy exchange serves to reduce back pressure to some extent.
As mentioned above, the invention is concerned with a windmill type of power plant which comprises a multiple-vane propellor unit rotating in a horizontal plane about a vertical axis. The horizontal propellor unit of the invention may be mounted on the top of an appropriate supporting structure. The propellor unit serves to drive an electric generator, pump, or instrumentality, positioned within the supporting structure, the drive being either direct of through an appropriate gear box.
The horizontal propellor unit of the invention comprises a hub with a plurality of vanes mounted for rotation about the hub. Each of the vanes has a webbing member of zig-zag shape positioned within an external shell to form a series of triangular shaped cells or pockets. The shell has a parabolic cross-section, with an open trailing edge, and with a leading edge of a symmetrical airfoil shape. The internal cells provide structural rigidity for the shell and reduce vortex disturbances due to angular airflow. The propellor unit of the invention responds to wind from any direction, so that there is no need for tracking mechanism to maintain the unit turned into the wind.
The propellor unit of the invention may be constructed of fiberglass, light metal, or any other suitable material. The unit is simple, light, and inexpensive, and it is easy to build and to install.